Find Captain Frederick Selous in Zanzibar.
He will ask you to collect the horn of a rhino, this can be found on the black rhino in the Savannah.
Once you give him the horn:
He will ask you to get a map. Go 3WN, Kneel in front of the statue; You will fall. Follow the path to its end, arriving in a room with a pentagram and Imp.
He will tell you to go get him a random item. Once you've found the item, return to the imp and give it to him (sit pentagram again).
Go give the map to Frederick.